In a typical cellular radio system, wireless user equipment units (UEs) communicate via a radio access network (RAN) with one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network. Alternatively, the wireless user equipment units can be fixed wireless devices, e.g., fixed cellular devices/terminals which are part of a wireless local loop or the like.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a radio base station. A cell is a geographical area where radio coverage is provided by the radio equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The radio base stations communicate over the air interface with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landline or microwave link) to a control node known as a base station controller (BSC) or a radio network controller (RNC). The control node supervises and coordinates various activities of connected plural radio base stations. The control node is typically connected to one or more core networks.
A conventional radio base station in a cellular communications system is generally located in a single location, and the distance between the baseband circuitry and the radio circuitry is relatively short, e.g., on the order of one meter. A distributed radio base station includes the radio equipment control (REC) and the radio equipment (RE). Both parts may be physically separated, (i.e., the RE may be close to the antenna, whereas the REC is located in a conveniently accessible site), or both may be co-located as in a conventional radio base station design. The radio equipment control (REC) performs baseband signal processing, and each radio equipment (RE) converts between baseband and radio frequencies and transmits and receives signals over one or more antennas. Each RE serves a certain geographic area, sector, or cell. Separate, dedicated optical and/or electrical links connect the radio equipment control (REC) to each of the plural remote radio equipment (RE). However, the term link as used hereafter refers to a logical link and is not limited to any particular physical medium. Each link carries digital information downlink from the REC to the RE and digital information uplink from the RE to the REC.
It would be desirable to have a standardized common interface between a REC and one or more REs. Such a standardized interface enables flexible and efficient product differentiation for radio base stations and independent technology evolution for the RE and REC. Such a standard would preferably define necessary items for transport, connectivity, and control including user plane data, control and management (C&M) plane transport mechanisms, and synchronization. Standardization would be particularly beneficial for hardware-dependent layers, e.g., physical layers, to ensure technology evolution on both sides of the interface with only a limited need for hardware adaptation. One advantageous result is that product differentiation in terms of functionality, management, and characteristics is not limited.
Other features that would be desirable to be supported by such an interface include:                Very high bandwidth utilization with the bandwidth supporting as many antenna-carriers as possible.        Very low delay (cable delay not included).        High-performance with respect to time and frequency distribution.        Flexible control and management signaling bandwidth.        Plug-and-play startup.        Flexible line bit rate        Flexible physical interface        
These features and others are achieved by an interface, apparatus, and method for communication between a radio equipment control (REC) node and a radio equipment (RE) node in a radio base station that transceives information over the radio interface using multiple antenna-carriers. The REC node is separate from and coupled to the RE node by a transmission link. Both control information and user information are generated for transmission over the transmission link from one of the REC node and the RE node to the other. The user information includes multiple data flows. Each data flow corresponds to data associated with one antenna per one radio carrier. The control and user information are formatted into multiple time division multiplexed (TDM) frames. Each basic TDM frame includes a control time slot for the control information and multiple data time slots for the user information. Each data time slot corresponds to a data flow of one of the antenna carriers. The frames are then transmitted over the transmission link to the other node. In an example implementation in a wideband code division multiple access (CDMA) environment, the time period of the frame corresponds to one CDMA chip time period.
Each antenna carrier has a corresponding time slot in the frame so that the data samples for each antenna carrier are inserted in the antenna carrier's corresponding time slot. The corresponding time slot position in the frame may be fixed or it may be variable. The control information includes multiple different control flows, and a portion of them is included in the control time slot. The different control flows may include, for example, four control flows: radio interface and timing synchronization information, control and management (C&M) information, layer 1 (L1) control information, and extension information. The control and management information includes both fast and slow control and management information, and the L1 signaling indicates the bit rate of both.
The control time slots may be arranged into 64 subchannels. Each such subchannel corresponds to every 64th control time slot. The 64 subchannels may then be allocated to carry the four control flows. Multiple basic frames may be combined into a hyperframe, and multiple hyperframes may be combined into a radio frame. One or more borders of the hyperframe are used to map each control time slot to a respective assigned subchannel. Each of the four control words within a hyperframe carries one subflow of a control flow.
The control information includes a known symbol for use in obtaining synchronization between the REC and the RE. The synchronization includes detecting the known symbol to retrieve one or more hyperframe borders. The known signal is periodically provided, and synchronization is obtained without requiring a feedback signal be sent in response to detecting the known signal. In one, non-limiting example implementation, the known signal is a K28.5 symbol.
Start-up communication between the REC and the RE include negotiations of one or more characteristics for the transmission link. The negotiations begin with the REC sending transmissions over the interface, with each transmission using one of several different line bit rates. The RE attempts to detect the line bit rate of each such transmission. If the RE detects one of the REC transmissions, then the RE replies to the REC using the same line bit rate. Similarly, one or both of the REC and RE transmit a highest, supported bit rate for one or more control and management flows. The node with the highest control and management bit rate adopts the highest rate supported by the other node. Alternatively, the REC proposes a lower C&M bit rate. A similar back-and-forth negotiation occurs with respect to the highest supported version of the REC-RE interface communications protocol.
Another feature includes calibrating or compensating for a transmission time delay associated with the transmission link/internal interface. More specifically, the RE obtains an RE time difference between when a frame structure is received from the REC and when the frame structure is transmitted to the REC. Similarly, the REC determines an REC time difference between when a frame structure is received from the RE and when the frame structure is transmitted to the RE. A round-trip delay is determined by subtracting the RE time difference and the REC time difference.
These features can be implemented for a single “hop” connection between an REC and an RE. But they also can be implemented for a “multi-hop” connection composed of an REC coupled to multiple RECs. To facilitate both single hop and multi-hop configurations, the terms master port and slave port are defined and used so that the interface is defined between a master port and a slave port rather than between an REC and an RE. As a result, each link connects two node ports which have asymmetrical functions and roles: a master and a slave. The ports of the REC are master ports. An RE has at least one slave port and optionally one or more master ports depending on whether it is coupled to another RE.
Multi-hop configurations present additional challenges as compared to single hop configurations, particularly in the area of synchronization. The handling of certain system-wide information is also important. Should certain information be passed onto the next RE node and should information not be passed onto the next RE node? Multiple advantages features are described to facilitate multi-hop base station configurations.
A multi-hop configured radio base station exchanges data between a radio equipment control (REC) node and first and second radio equipment (RE) nodes for transceiving information over a radio interface using multiple antenna carriers. The REC node is separate from and coupled to the first RE node by a first transmission link. The first RE node is separate from and coupled to the second RE node by a second transmission link. Control information and user information are provided for transmission over the first transmission link from the REC node to the first RE node, and that information intended for the second RE is forwarded over the second transmission link from the first RE node to the second RE node.
The control information includes layer 1 (L1) signaling, and the L1 signaling includes a service access point defect indicator (SDI) that indicates whether higher layers are operational for data, synchronization, or control and management (C&M). In multi-hop configuration, when the first RE #1 receives the SDI over the first transmission link, the RE #1 ignores the data received over the first transmission link, and forwards the SDI over the second transmission link to the second RE #2. Alternatively, when the first RE #1 receives the SDI over the first transmission link, the first RE node can transmit data received on a redundant first transmission link over the second transmission link to RE #2. Also, if the control information sent by the REC includes a reset indicator, the first RE #1 initiates a reset operation for the first RE #1 and also sends the reset indicator to the second RE #2.
Time delay calibration for multi-hop configuration is more complicated than for single hop. In general, a first transmission time delay associated with the first transmission link and a second transmission time delay associated with the second transmission link are determined. The first and second transmission delays are used to determine in a loop delay associated with the REC node, the first RE #1, and the second RE #2.
An example more detailed time delay compensation scheme for multi-hop includes each RE providing the REC with a time offset between the RE's input slave port and output slave port. The REC transmits a first frame synchronization signal to the first RE at a first time. The first RE provides the REC with a downlink delay associated with receiving a first frame synchronization signal on its input slave port and transmits the first frame synchronization signal on its output master port. The first RE provides the REC with an uplink delay associated with receiving a second frame synchronization signal on its input master port and transmits a third frame synchronization signal on its output slave port. The REC receives the third frame synchronization signal at a second time and determines a time difference between the first and second times. Ultimately, the REC determines a first transmission time delay associated with the first transmission link and a second transmission time delay associated with the second transmission link based on the time difference, the downlink delay, the uplink delay, and each time offset.
These and other features and advantages are further described in connection with the figures and the detailed description.